Preprints  

SHRIMP (Sensitive High Resolution Ion MicroProbe) is a instrument that for decades has used the radioactive decay of uranium into lead to measure geologic time. The accuracy adn precision of this instrument has not been seriously reviewed in almost 20 years. This paper compares several dozen SHRIMP ages in our database with more accurate and precise methods to assess SHRIMP accuracy and precision. Analytical and geologic complications are addressed to try to improve the method.

If topographical obstructions are present in the surroundings of sampling sites, exposure ages of rock surfaces need to be corrected. A toolbox for the ESRI ArcGIS software allows for quantifying topographic shielding with a digital elevation model, but it has only been validated with few field data. In this study, the output of the toolbox is evaluated with a more extensive dataset. If suitable elevation data is chosen, the toolbox provides a sound approach to determine topographic shielding.

Acid leaching is commonly used to remove damaged portions of zircon crystals prior to U-Pb dating. However, a basic understanding of the microstructural processes that occur during leaching is lacking. We present the first 3D view of zircon dissolution based on X-ray computed tomography data acquired before and after acid leaching. These data are paired with images of etched grain surfaces and Raman spectral data. We also reveal exciting opportunities for imaging radiation damage zoning in 3D.

In situ ¹⁴C’s short half-life (5.7 ky) is unique among cosmogenic nuclides, making it sensitive to complex exposure/burial histories since 25 ka. Current extraction methods focus on quartz, but the ability to extract it from other minerals would expand applications. We developed MATLAB^® scripts to calculate in situ ¹⁴C production rates from a broad range of mineral compositions. Results confirm O, Si, Al, and Mg as key targets, but also find significant production from Na for the first time.

Deposits left behind by past glacial activity provide insight into the previous size and behavior of glaciers, and act as another line of evidence for past climate. Here we present new age control for glacial deposits in the mountains of Montana and Wyoming, United States. While some deposits indicate glacial activity within the last 2000 years, others are shown to be older than previously thought, thus redefining the extent of regional Holocene glaciation.

We constrained deposition phases of fluvial sediments (NE Belgium) over the last 1 Ma with analysis and modelling of rare isotopes accumulation within sediments, occuring in function of time and inverse function of depth. They allowed the determination of 3 superposed deposition phases and intercalated non-deposition periods of ~ 40 kyr each. These phases correspond to 20% of the sediment age, which highlights the importance to consider deposition phase when dating fluvial sediments.

There is currently no standardized method of performing uncertainty propagation in the (U-Th)/He system, causing difficulties in data interpretation. We present two methods of uncertainty propagation and describe a free, open-source software (HeCalc) to apply these methods. A compilation of real data using only analytical uncertainty, and 2 % and 5 % uncertainties in F_T yields respective median relative date uncertainties of 2.9 %, 3.3 % and 5.0 % for apatites and 1.7 %, 3.3 % and 5.0 % for zircons.

We developed code to automatically and semi-automatically measure dimensions of detrital mineral grains in reflected light images saved at LA-ICP-MS facilities that use Chromium targeting software. Our code uses trained deep learning models to segment grain-images with greater accuracy than is possible using other image segmentation techniques. We implement our code in user-accessible, ready-to-run Google Colab notebooks, links to which can be found at https://github.com/MCSitar/colab_zirc_dims.

Apatite helium thermochronology is a method used for dating the time at which a rock (and the apatite crystals contained within) cooled below a certain temperature, by measuring radioactive parent isotopes (uranium and thorium) and daughter isotopes (helium). This paper proposes a revision to a commonly used calculation that corrects raw data to account for instances when the analyzed apatite crystals are fragmented. It demonstrates the improved accuracy and precision of the proposed revision.

We proposed a new non-destructive mineralogical methodology on inframilimetric grains that allows to quantify the hematite and goethite content and hematite/goethite ratio of grains prior to (U-Th)/He geochronological analysis. (U-Th)/He data performed on different aliquots with different acquisition time shows no remarkable differences in age, opening a new way to investigate the (U-Th)/He data evolution in supergene lateritic duricrusts.

The U-Pb dating by in situ laser ablation mass spectrometry (LA-ICPMS) technique requires reference materials of the same nature as the samples to be analysed. Here, we have explored the suitability of using carbonate materials as reference for sulfates, since there is no sulfate reference material. The results we obtained are satisfactory and thus, from now on, the sulfates can also be analysed.

Cryogenic cave carbonates (CCCs) provide a marker for past permafrost conditions. Their formation age is determined by ²³⁰Th/U dating. However, samples can be contaminated with small amounts of ²³⁰Th at formation, which can cause inaccurate ages and requires correction. We analysed multiple CCCs and found that varying degrees of contamination can cause an apparent spread of ages, when really all samples formed within a single freezing event. A statistical correction method is presented.

Advancements in technology allow for new techniques to date rocks quicker, cheaper, and with little sample preparation. A unique use of this method is to date carbon-rich siltstones and constrain when these rocks were first deposited. This approach can also time when these sequences are subsequently affected by heat or fluids after they were deposited. This is useful, as the formation of metal-bearing fluids or petroleum source rocks is commonly associated with such processes.

Secondary Ion Mass Spectrometer (SIMS) is the oldest and most sensitive analytical technique for in-situ U-Pb geochronology. This paper introduces a new algorithm for SIMS data reduction that treats the data as 'compositional data', which means that the relative abundances of ²⁰⁴Pb, ²⁰⁶Pb, ²⁰⁷Pb and ²³⁸Pb are processed within a tetrahedral data space or 'simplex'. The new method is implemented in an eponymous computer program that is compatible with the two dominant types of SIMS instruments.

Chemical weathering alters the chemical composition of mineral grains, and it follows that luminescence dating signals may also be progressively modified. We artificially weathered feldspar samples under different chemical conditions to understand the effect of feldspar partial dissolution on their luminescence properties. Only minor changes were observed on luminescence dating properties, implying that chemical alteration of feldspar surfaces may not affect luminescence dating signals.

We apply quartz ³He paleothermometry along two deglaciation profiles in the European Alps to reconstruct temperature evolution since the Last Glacial Maximum. We observe a ³He thermal signal clearly colder than today in all bedrock surface samples exposed prior the Holocene. Current uncertainties in ³He diffusion kinetics do not permit to distinguish if this signal results from Late Pleistocene ambient temperature changes or from recent ground temperature variation due to permafrost degradation.

Noble gases are largely excluded from minerals during rock formation, but they are produced by certain radioactive decay schemes and trapped in mineral lattices. However, they are present in the atmosphere, which means that they can be adsorbed or trapped by physical processes. We present details of a troublesome trapping mechanism for helium during sample crushing and show when it can be ignored and how it can be easily avoided during common laboratory procedures.

When first introduced together with the depth profile technique to determine the surface exposure age, the linear inversion approach has suffered with the drawbacks of not incorporating erosion and muons into calculation. In this paper, we increase the accuracy and applicability of linear inversion approach by fully considering surface erosion, muogenic production, and radioactive decay, while maintain its advantage of being straightforward to apply to determine an exposure age.

This paper outlines a method that helps mineral explore for gold. When can see the alteration caused by the mineralising fluids, it is possible to use geochemical methods to vector towards the deposit. But such methods failed at Martabe. We decided to work out why. Our results showed that there were several distinct and separate very short-lived alteration events. The answer might be that vectoring is possible only when samples are compared from the same mineralising system.

Paleomagnetic data from Cascade Lake (Brooks Range, Alaska) extend the radiometric-based age model of the sedimentary sequence extending back 21 kyr. Correlated ages based on prominent features in paleomagnetic secular variations (PSV) diverge from the radiometric ages in the upper 1.6 m, by up to about 2000 years at around 4 ka. Four late Holocene cryptotephra in this section support the PSV chronology and suggest the influence of hard water or aged organic material.

Mineral grains within sediment or rock absorb a radiation dose from the decay of radionuclides in the host matrix. For the beta dose component, the estimated dose rate must be adjusted for the attenuation of beta particles within the mineral grains. We show here that the mean dose rate to dosimeter grains in a granular matrix is dependent on the grain-size distributions of the source grains, and of the bulk sediment, as well as on the grain size of the dosimeters.

Prehistoric volcanic eruptions are often dated by wiggle matching series of radiocarbon ages on tree rings to standard calibration curves, ignoring potential contamination by 'old' carbon given off by the volcano. We modeled the effects of low amounts of contamination on wiggle match dates for the 10th century Changbaishan eruption and found evidence of contamination in all. We propose a new protocol to identify the presence of contamination, and provide more secure dates for major eruptions.

The timing and duration of fluid activity within a gold deposit enables a greater understanding of how the deposit evolved and thus help future mineral exploration. This research uses high resolution dating methods to unravel the overprinting fluid activity at the Martabe gold field in Sumatra. Methods outline in this report can be applied to deposits globally.

Potassium-based geochronology, including the ⁴⁰Ar/³⁹Ar and K-Ar methods, provides critical constraints on the timing and duration of many events and processes in earth history. These methods assume that a key parameter, the fraction of potassium with a mass of 40, does not vary in some relevant materials. Some recent work has identified some variability in these materials. This work examines the effects of this variability on calculated K-Ar and ⁴⁰Ar/³⁹Ar ages.